1. Field of the Invention
This invention relates to organometallic compounds. More particularly, it relates to organometallic stabilizers made from a C.sub.21 -cycloaliphatic dicarboxylic acid and used to reduce degradation of polyvinyl halide resin compositions.
2. The Prior Art
Polyvinyl chloride degradation is facilitated under conditions of elevated temperature and prolonged processing. The mechanism of degradation is a dehydrochlorination reaction. Polyvinyl chloride is a complex mixture of both straight and branched chains. Ideally, the vinyl chloride monomer polymerizes in a regularly ordered, repeating head-to-head monomer. However, termination of the polymer chain is responsible for a number of different end-group structures and internal anomalies.
The degradation of polyvinyl chloride is due initially to the "popping out" of an HCl molecule, which may be brought about by heat, from an [allylic] chlorine atom which then acts as an activating group as shown in the following sequence wherein X is the activating group:
[1] -- CH.sub.2 -- CHCl -- CH.sub.2 -- CHCl -- CH.sub.2 -- CHCl -- X -- PA0 [2] -- ch.sub.2 -- chcl -- CH.sub.2 -- CHCl -- CH = CH -- X -- PA0 [3] -- ch = ch -- ch = ch -- ch = ch -- x --
The elimination of the first HCl molecule and the subsequent formation of an unsaturated double bond on the polyvinyl chloride polymer chain activates the neighboring chlorine atom (allylic), initiating the unzippering of the chain. As heat induced degradation reaches its later stages, darkened color and detrimental physical changes occur.
Metal soaps, organotin compounds, and epoxides have been found to be the most effective stabilizers in combating polyvinyl chloride degradation. The ideal polyvinyl chloride stabilizer should not only retard heat and mechanical degradation but also resist light and oxidative actions. The stabilizer apparently disrupts the chain-reaction polyene formation and thwarts the elimination of HCl from the vinyl chloride polymer. The metal soap is capable of absorbing the HCl evolved and "repairing" the segment of the damaged polymer by ester exchange. Thus, the chlorine atoms lost from the polymer chain are replaced by ester groups from the soap. A review of polyvinyl chloride entitled "PVC Primer" may be found in Plastics Engineering, Vol XXIX, No. 12, pp. 26-40 (Dec. 1973).
Thus, it is an object of this invention to provide novel organometallic compounds made from a C.sub.21 -cycloaliphatic dicarboxylic acid. Another object of this invention is to provide vinyl halide polymer compositions containing the novel organometallic stabilizers. Other objects, features and advantages of this invention will be evident from the following detailed description.